In recent years, the demand for not only a reduction in the size of an imaging optical system but also a higher resolution has been increasing. To realize a reduction in the light-receiving region and an increase in the number of pixels at the same time, it is necessary to decrease the unit pixel size.
With this backdrop, a solid-state imaging device has been proposed in which a plurality of n-type diffusion layers are provided in the depth direction of an Si substrate and signal charges of different colors are accumulated in the individual diffusion layers. With the device, it is possible to obtain color information three times that offered by conventional pixels per unit Si area. However, since three adjacent signal accumulation regions are provided in the same Si substrate, electrons photoelectrically converted in the Si substrate flow in between laterally adjoining signal accumulation regions due to thermal diffusion. This results in a decrease in the resolution and color mixture in reproduced images, which deteriorates the image quality. Moreover, since both the photoelectric conversion region and the signal scanning region are provided in the same Si substrate, the area ratio of the photoelectric conversion region to the unit pixel size decreases, resulting in a decrease in the sensitivity.
In addition, a solid-state imaging device has been proposed in which a three-layer photoelectric conversion film sandwiched between transparent electrodes is provided above an Si substrate that includes an accumulation diode and a signal read circuit and a different color signal charge is accumulated in each of the individual photoelectric conversion films. In the device, photoelectrons generated at the photoelectric conversion film are accumulated temporarily in the accumulation diode via metal interconnections and then read by a signal scanning circuit. Consequently, three color signals can be obtained per unit pixel. However, since the metal interconnections are connected directly to the photoelectric conversion film, noise, such as kTC noise, is generated. As a result, a lot of noise is generated in reproduced images.